This invention relates generally to the field of electric heating units, and more particularly relates to radiant heating units for use in ranges or cooktop units.
In U.S. Pat. No. 5,968,391 to Deo et al, entitled xe2x80x9cModular Electric Heating Unit,xe2x80x9d there is disclosed a radiant heater unit usable as a replacement part for conventional tubular coil heating units commonly found in residential stoves and cooktop units. The heater disclosed in the Deo ""391 patent incorporates a resistive wire radiant heating element within a pan defining the bottom and sides of the module unit. A heat-conductive glass cover or top is disposed over the radiant heating element in a spaced relationship, defining a cavity of air within the pan. In one embodiment, the modular heating unit is adapted for installation in a xe2x80x9cdrop-inxe2x80x9d manner, such that it may be utilized both in original equipment or as a replacement for a conventional coil-type tubular stovetop heating element. The Deo ""391 patent is commonly assigned to the assignee of the present invention, and is hereby incorporated by reference herein in its entirety.
In U.S. Pat. No. 5,954,981 to Deo et al., entitled xe2x80x9cMounting Apparatus for Modular Radiant Heating Element,xe2x80x9d there is disclosed a bracket for mounting a modular radiant heating element within an opening in a cooktop. The Deo ""981 patent is also commonly assigned to the assignee of the present invention and is also incorporated by reference herein in its entirety.
In the Deo ""391 patent, the resistive wire radiant heating element is disposed upon a cake of microporous insulating material disposed on the bottom surface of the pan in a desired serpentine pattern. U.S. Pat. No. 5,935,469 to Deo et al., entitled xe2x80x9cInsulating Staple for Holding the Resistive Member of a Heating Element in Place,xe2x80x9d and U.S. Pat. No. 5,977,524 to Deo et al., entitled xe2x80x9cMicrowire Staple for Holding the Resistive Member of a Heating Element in Place,xe2x80x9d each disclose the use of small-diameter staples to hold the resistive wire in place atop the insulating cake. The Deo ""469 and ""524 patents are commonly assigned to the assignee of the present invention and are hereby incorporated by reference herein in their respective entireties.
Modular radiant heating elements such as that disclosed in the above-referenced Deo ""391 patent are believed to offer significant advantages over prior radiant cooktop designs. One significant advantage is that in many radiant cooktop implementations, a single piece of glass extends over the entire surface area of the cooktop. If the glass in such implementations is damaged, the entire cooktop surface must be replaced. With the modular units disclosed in the Deo ""391 patent, each heating element is separately and independently serviceable. The modular design proposed in the ""391 patent further advantageously allows the heating elements to be retrofitted into existing stoves or ranges, replacing the conventional coiled tubular elements often found in such units.
Notwithstanding the perceived advantages of the radiant heater technology disclosed in the various above-referenced patents, it is believed that there is room for even further improvements and developments in this radiant heater technology. One issue relates to the thermal efficiency of radiant heaters. In particular, it is desirable for the heat radiating from the heater wire to be directed as much as possible directly upward toward the glass cover. Heat dissipated out of the sides or bottom of the heating unit will undesirably reduce the unit""s overall efficiency.
Another consideration relates to durability of the glass top of the heating unit. To qualify for certain safety and quality ratings (for example, certification by Underwriter""s Laboratories), a modular heating element must be able to withstand physical stresses up to some extent. For example, in the case of glass-topped cooktops, one test is UL 858 Section 71.3 that involves dropping a steel sphere, 2 inches in diameter and weighing 1.18 lbs., from 20.25 inches above the cooktop.
The present invention is directed to overcoming, or at least reducing the effects of, one or more of the problems set forth above.
In view of the foregoing considerations, the present invention is directed to a modular heating element constructed so as to maximize its thermal efficiency and resistance to breakage.
To this end, the present invention includes a modular radiant heating unit having a pan, a radiant heating element, a thermally insulating support element, an insulation ring, a glass-ceramic plate, and a thermally insulating gasket. The pan has a bottom and a circumferential sidewall. The circumferential sidewall has a flanged upper rim. The radiant heating element is disposed on the thermally insulating support element that rests on the bottom of the pan. The insulation ring extends around the inner surface of the circumferential sidewall. The thermally insulating gasket is disposed beneath the glass-ceramic plate and between the plate and the flanged upper rim.
The gasket functions to minimize radial heat dissipation, thereby minimizing thermal stress on the sealant used to affix the plate to the pan defining the body of the heating unit. The gasket is readily compressible, such that when pressed against the dimpled underside of the glass cover plate on its top side and against the insulation ring on its bottom side, the gasket readily conforms itself simultaneously to both of these surfaces and provides an easily-developed seal to minimize heat loss across those surfaces. Moreover, the gasket makes the heating unit more durable by serving as a cushion between the plate and the pan as well as the more rigid insulation ring.
In another embodiment, the present invention includes a heating unit adapted to be installed in a cooktop. The heating unit includes a pan, a thermally insulating support element, an insulation ring, and a thermally insulating gasket. The pan has a bottom and a circumferential sidewall. The thermally insulating support element is disposed on the bottom of the pan. The heating element generates heat and is disposed on the thermally insulating support and beneath a glass-ceramic cooking plate. The insulation ring extends around the inner surface of the circumferential sidewall. The thermally insulating gasket is disposed beneath the glass-ceramic cooking plate and between the glass-ceramic cooking plate and the insulation ring.
The present invention further includes a method of assembling a modular radiant heating unit. The method includes the steps of: disposing a thermally insulating support element in a bottom of an open-topped pan having a circumferential sidewall and a flanged upper rim; disposing a radiant heating element in a pattern upon the insulating support element; disposing an insulation ring in the pan so as to extend around and adjacent to the circumferential sidewall; disposing a thermally insulating washer-like gasket upon the insulation ring; and disposing a glass-ceramic plate having an upper surface defining a cooktop over the open top of the pan such that the gasket is disposed between the plate and the insulating ring and between the plate and the flanged upper rim. The method may further include the steps of introducing a thermal sealant between the plate and the flanged upper rim adjacent to the gasket and applying compressive pressure upon an upper surface of the plate, thereby compressing the gasket between the plate and the insulation ring and between the plate and the flanged upper rim.